Construction And Application Of Microfluidic Devices For Sperm Screening And In Vitro Fertilization

In vitro fertilization (IVF) technology has been broadly applied to solve human infertility during the past three decades. While huge successes in practice and breakthroughs in technology have been achieved, several problems remain to be addressed, including:1) The swim-up method, an assay on sperm motility, is used clinically to select the ideal sperm for subsequent manipulation. However, additional parameters, including chemotaxis, and thermotaxis are somehow underestimated in sperm health evaluation. 2) The in vitro fertilization condition and embryo culture environment is far from similar to in vivo conditions and the technical complexity involved in the manual procedures could cause potential adverse impacts on the embryos. Microfluidic technology provides an alternative solution for these issues. Accordingly, we are aimed to construct different microfluidic platforms to address three main issues: 1) We optimized the width, length and depth of a straight channel as well as the time point for sperm collection to improve the efficiency of sperm screening on a microfluidic device. The sperm motility and relative sperm count in the outlet pool was evaluated and we found a straight channel 7 mm in length, 1 mm in width and 100μm in depth showed the best performance and the appropriate time point for sperm collection was between 15-30 minutes. 2) To monitor both sperm motility and chemotaxis simultaneously during sperm screening, we designed and constructed a microdevice comprising a straight channel connected with a bi-branch channel that mimics the mammalian female reproductive tract. Cumulus cells were selectively cultured in the bi-branch channel to generate a chemoattractant-forming chemical gradient. Sperm chemotaxis was represented by the ratio of the sperm swimming towards different branches. About 10% of sperms were found chemotactically responsive in our experiment, which is consistent with previous studies. 3) We developed a microdevice to mimic genital tract function by integrating each step of IVF, including: oocyte positioning, sperm screening, fertilization, medium replacement and embryo culture. Oocytes could be singly positioned in a 4×4 array of octa-column units. The four symmetrical straight channels, crossing at the oocyte positioning region, could perform efficient motile sperm selection and facilitate rapid medium replacement. The fertilization process and early embryonic development of individual zygote was traced with microscopic recording and in situ fluorescent staining. The murine sperm motility was increased from 60.8±3.4% to 96.1±1.9% through the screening channels. The embryo growth rate as well as blastocyst formation were similar between the routine Petri dish group and the microdevice group (p>0.1).In summary, the combined evaluation of both sperm motility and chemotaxis was achieved on our microchannel, and the motile and chemotactically responsive sperms can be easily enriched on a lab-on-a-chip device to improve IVF outcome. The microdevice for IVF provides an integrated system for human in vitro fertilization and animal embryo production with advantages of reduction of manual manipulation and adverse cellular impacts.